Gruber (U.S. Pat. No. 4,912,092) described prophylactic administration of AICA riboside compounds, including analogs and prodrugs thereof, to prevent tissue damage associated with undesired decreased blood flow. The AICA riboside compounds are administered in amounts between 0.1 and 500 mg/kg/day. AICA riboside's prodrugs, including those set forth in the commonly assigned U.S. Pat. No. 5,082,829, entitled “AICA Riboside Prodrugs,” U.S. application Ser. No. 07/408,107, filed Sep. 15, 1989, entitled “Methods and Compounds for AICA Riboside Delivery and for Lowering Blood Glucose,” and U.S. application Ser. No. 07/466,979, filed Jan. 18, 1990, entitled “Method and Compounds for AICA Riboside Delivery and for Lowering Blood Glucose,” all of which are incorporated herein in their entireties by this reference, may also be administered. Certain prodrugs of AICA riboside are defined therein, and generally are compounds which, when introduced into the body, will metabolize into AICA riboside or an active metabolite, for example, AICA riboside monophosphate. Other prodrugs include mono-, di- and tri-5′ phosphates of AICA riboside.
Adenosine, 9-β-D-ribofuranosyladenine (the nucleoside of the purine adenine), belongs to the class of biochemicals termed purine nucleosides and is a key biochemical cell regulatory molecule, as described by Fox and Kelly in the Annual Reviews of Biochemistry, Vol. 47, p. 635, 1978. It interacts with a wide variety of cell types and is responsible for a myriad of biological effects. For instance, adenosine is a potent vasodilator, an inhibitor of immune cell function, and can at certain levels enhance activation of mast cells, is an inhibitor of granulocyte oxygen-free radial production, is anti-arrhythmic, and is an inhibitory neurotransmitter. Considering its broad spectrum of biological activity, considerable effort has been aimed at establishing practical therapeutic uses for adenosine and its analogs.
Since adenosine is thought to act at the level of the cell plasma membrane by binding to receptors anchored in the membrane, past work has included attempts to increase extracellular levels of adenosine by administration of it into the blood stream. Unfortunately, adenosine is toxic at concentrations that have to be administered to a patient to maintain an efficacious extracellular therapeutic level, and the administration of adenosine alone is therefore of limited therapeutic use. Further, adenosine receptors are subject to negative feedback control following exposure to adenosine, including down-regulation of the receptors.
Other ways of achieving the effect of a high local extracellular level of adenosine exist and have also been studied. They include: (a) interference with the uptake of adenosine with reagents that specifically block adenosine transport, as described by Paterson et al., in the Annals of the New York Academy of Sciences, Vol. 255, p. 402 (1975); (b) prevention of the degradation of adenosine, as described by Carson and Seegmiller in The Journal of Clinical Investigation Vol. 57, p. 274 (1976); and (c) the use of analogs of adenosine constructed to bind to adenosine cell plasma membrane receptors.
There are a large repertoire of chemicals that can inhibit the cellular uptake of adenosine. Some do so specifically and are essentially competitive inhibitors of adenosine uptake, and others inhibit nonspecifically. P-Nitrobenzylthionosine appears to be a competitive inhibitor, while dipyridamole and a variety of other chemicals, including colchicine, phenethylalcohol and papaverine inhibit uptake nonspecifically.
Extracellular levels of adenosine can be increased by the use of chemicals that inhibit enzymatic degradation of adenosine. Previous work has focused on identifying inhibitors of adenosine deaminase, which participates in the conversion of adenosine to inosine. Adenosine deaminase activity is inhibited by coformycin, 2′-deoxycoformycin, and erythro 9-(2-hydroxy-3-nonyl)adenine hydrochloride.
A number of adenosine receptor agonists and antagonists have been generated having structural modifications in the purine ring, alterations in substituent groups attached to the purine ring, and modifications or alterations in the site of attachment of the carbohydrate moiety. Halogenated adenosine derivatives appear to have been the most promising as agonist or antagonist and, as described by Wolff et al. in the Journal of Biological Chemistry, Vol. 252, p. 681, 1977, exert biological effects in experimental systems similar to those caused by adenosine.
Although all three techniques discussed above may have advantages over the use of adenosine alone, they have several disadvantages, the major disadvantages being that they rely on chemicals that have adverse therapeutic side effects, primarily due to the fact that they must be administered in doses that are toxic, and that they affect nonselectively most cell types. As described in Purine Metalolism in Man, (eds. De Bruyn, Simmonds and Muller), Plenum Press, New York, 1984, most cells in the body carry receptors for adenosine. Consequently, the use of techniques that increase adenosine levels generally throughout the body can cause unwanted, dramatic changes in normal cellular physiology.
With respect to post ischemic myocardial tissue and adenosine, it is stated in Swain, J. L., J. J. Hines, R. L. Sabina, and E. W. Holmes, Circulation Research 51:102-105 (1982), and in Holmes et al., U.S. Pat. No. 4,575,498 (issued Mar. 11, 1986), that adenosine concentration and blood flow are not altered in ischemic canine hearts exposed to the purine nucleoside 5-amino-4-imidazolecarboxamide riboside (AICA riboside). They also state that depletion of purine nucleotide pools, especially adenosine triphosphate (ATP), has been postulated to play a role in such dysfunction following, e.g., an ischemic event, and claim to have demonstrated an enhanced nucleotide synthesis and concomitant repletion of ATP pools by treating post-ischemic myocardium with the purine analog AICA riboside, stating that repletion of ATP pools should, in theory, enable the amelioration of tissue damage.
Several other groups of investigators, however, have published studies in which they were unable to demonstrate an enhanced repletion of ATP pools in ischemic tissue by the method of Swain et al., supra. Mentzer, R. M., Ely, S. W., Lasley, R. D., Lee, B. K. and Beme, R. M., Fed. Proc. 43:903 (1984); Mitsos, S. E., S. R. Jolly and B. R. Lucchesi, Pharmacology 31:121-131 (1985); Hoffineister, H. M., Nienaber, C., Mauser, M. and Schaper, W. E., Basic Research in Cardiology 80:445-458 (1985); Mauser, M., H. M. Hoffineister, C. Nienaber, and W. E. Schaper, Circul. Res. 56:220-230 (1985). In fact, Hoffmeister et al. demonstrate that ATP repletion by another mechanism does not improve cardiac dysfunction. Even Holmes and Swain have documented that AICA riboside does not effectively reach ATP because of an inhibition of the conversion of inosine monophosphate (IMP) to adenosine monophosphate (AMP). Sabina, R. L., Kemstine, K. H., Boyd, R. L., Holmes, E. W. and Swain, J. L., J. Biol. Chem. 257:10178 (1982); Amidon, T. M., Brazzamano, S., Swain, J. L., Circ. Suppl. 72:357 (1985); Swain, J. L., Hines, J. J., Sabina, R. L., Harburg, O. L. and Holmes, E. W., J. Clin. Invest. 74:1422-1427 (1984). Amidon et al., supra, state that “These results indicate that adenylosuccinate synthetase and/or lyase activities are limiting in isolated hearts and suggest that interventions designed to bypass IMP in AN (Adenine Nucleotide) synthesis might be more advantageous for increasing AN pool size.” Swain et al., supra., (J. Biol. Chem.), also demonstrated that AICA riboside does not consistently alter ATP levels in non-ischemic myocardium.
While Mitsos et al., supra claimed that their study demonstrated that AICA riboside infused intracoronary in high doses protected globally ischemic hearts from the mechanical dysfunction associated with an ischemic insult, Hoffineister et al., Basic Res. Cardiol. 80:445-458 (1985), showed that on producing a reversible ischemia in dogs by coronary artery occlusion, AICA riboside application did not improve postischemic function and, in fact, worsened it. Swain et al., supra (J. Clin. Invest.) confirms the detrimental effects of high doses of AICA riboside on muscle contractility. Thus, the proposal that the administration of AICA riboside would be of benefit to patients after an ischemic event for repletion of ATP pools does not appear to be valid.
It will be appreciated from the foregoing discussion that a technique that would increase extracellular levels of adenosine or adenosine analogs at specific times during a pathologic event, that would increase these compounds without complex side effects, and which would permit increased adenosine levels to be selectively targeted to cells that would benefit most from them would be of considerable therapeutic use. By way of example, such a technique would be especially useful in the prevention of, or response during, an ischemic event, such as heart attack or stroke, or other event involving an undesired, restricted or decreased blood flow, such as atherosclerosis, for adenosine is a vasodilator and prevents the production of superoxide radicals by granulocytes. Such a technique would also be useful in the prophylactic or affirmative treatment of pathologic states involving increased cellular excitation, such as (1) seizures or epilepsy, (2) arrhythmias, and (3) inflammation due to, for example, arthritis, autoimmune disease, Adult Respiratory Distress Syndrome (ARDS), and granulocyte activation by complement from blood contact with artificial membranes as occurs during dialysis or with heart-lung machines. It would further be useful in the treatment of patients who might have chronic low adenosine such as those suffering from autism, cerebral palsy, insomnia and other neuropsychiatric symptoms, including schizophrenia. The compounds useful in the invention, which include AICA riboside, may be used to accomplish these ends.
Another area of medical importance is the treatment of allergic diseases, which can be accomplished by either preventing mast cells from activating, or by interfering with the mediators of allergic responses which are secreted by mast cells. Mast cell activation can be down-regulated by immunotherapy (allergy shots) or by mast cell stabilizers such as cromalyn sodium, corticosteroids and aminophylline. There are also therapeutic agents which interfere with the products of mast cells such as anti-histamines and adrenergic agents. The mechanism of action of mast cell stabilization is not clearly understood. In the case of aminophylline, it is possible that it acts as an adenosine receptor antagonist. However, agents such as cromalyn sodium and the corticosteroids are not as well understood.
It will be appreciated, therefore, that effective allergy treatment with compounds which will not show any of the side effects of the above-noted compounds, such as drowsiness in the case of the anti-histamines, agitation in the case of adrenergic agents, and Cushing disease symptoms in the case of the corticosteroids, would be of great significance and utility. In contrast to compounds useful in the invention, such as AICA riboside and ribavirin, none of the three known mast cell stabilizers are known or believed to be metabolized in the cell to purine nucleoside triphosphates or purine nucleoside monophosphates.
Gruber (U.S. Pat. No. 5,817,640) described particular therapeutic concentrations of AICA riboside for the prevention of tissue damage associated with decreased blood flow in humans, and the determination of dosages which achieve efficacy while avoiding undesirable side effects. In one aspect, the AICA riboside or a prodrug thereof is administered to a person in an amount, which maintains a blood plasma concentration of AICA riboside for a sufficient time so that the risk of tissue damage is reduced in that person, of from about 1 ug/ml to about 20 ug/ml. In another aspect, the AICA riboside is administered to a person at a dosage of from about 0.01 mg/kg/min to about 2.0 mg/kg/min to reduce the risk of tissue damage. Another aspect features the prevention of tissue damage by administering a total dosage of AICA riboside of from 10 mg/kg to 200 mg/kg.
AICA riboside enters cells and is phosphorylated to AICA riboside monophosphate (“ZMP”), a naturally occurring intermediate in purine biosynthesis. AICA riboside increases extracellular adenosine levels under conditions of net ATP breakdown and, therefore, in light of the cardioprotective and neuroprotective properties of adenosine it may have potential therapeutic uses. However, AICA riboside has a relatively low potency and short half life. Also, we have found that AICA riboside does not cross the blood-brain barrier well and is inefficiently absorbed from the gastrointestinal tract. These characteristics of limited potency, limited oral bioavailability and limited brain penetration decrease its potential for use as a therapeutic agent.
AICA riboside treatment has been reported to have beneficial effects in a number of experimental models of myocardial ischemia. In a dog model, in which pacing induced a profound progressive decline in wall thickening and endocardial blood flow and an increase in ST segment deviation of the intramyocardial EKG, AICA riboside markedly attenuated these changes to maintain contractile function> Young and Mullane, Am. J. Physio., in press (1991)!. In another dog model, in which ischemia was induced by coronary artery occlusion, AICA riboside was reported to be beneficial by significantly decreasing ischemia-induced arrhythmias and improving blood flow to the ischemic region of the myocardium (Gruber et al, Circulation 80 (5): 1400-1410 (1990)). An effect of AICA riboside to increase regional blood flow and maintain contractile function was also reported in a dog model of coronary embolization in which ischemia was induced by administration of microspheres directly into the coronary circulation (Takashima et al, Heart and Vessels 5 (Supplement 4): 41 (1990)). A potential consequence of this reported redistribution in blood flow by AICA riboside was said to be a reduction of infarct size (McAllister et al, Clinical Research 35: 303A (1987)). Treatment with AICA riboside has been reported to have favorable consequences in other experimental models of myocardial ischemia. For instance, Mitsos et al (Pharmacology 31: 121-131 (1985)) reported that AICA riboside improved the recovery of post-ischemic function in the isolated blood-perfused cat heart and Bullough et al. (Jap. J. Pharmacol 52: 85p (1990)) reported improved recovery in an isolated buffer-perfused guinea pig heart. Thus, AICA riboside has been reported to alleviate ischemia-induced injury to the heart in various experimental models.
AICA riboside has also been reported to protect brain tissue from damage in two different experimental models of cerebral ischemia. In a gerbil model of global ischemia, AICA riboside was reported to prevent the degeneration of hippocampal CA-1 cells, which in control animals were virtually completely destroyed (Phillis and Clough-Helfman, Heart and Vessels 5 (Supplement 4): 36 (1990)). In a rat model of focal ischemia, AICA riboside treatment was reported to provide a significant reduction in infarct size. The protective effects of AICA riboside have also been reported in other models of ischemia, including rat skin flap survival (Qadir et al, Fed Proc. A626 (1988); Salemo et al in Proceedings of 35th Annual Meeting of the Plastic Surgery Research Council, pp. 117-120 (1990)) and gastro-intestinal ischemia-reperfusion injury (Kaminski & Proctor, Circulation Res. 66 (6): 1713-1729 (1990)).
A number of studies suggest that the beneficial effects of AICA riboside can be ascribed, at least in part, to an increase in local levels of adenosine, which has similar cardioprotective (Olafsson et al, Circulation 76: 1135-1145 (1987)) and neuroprotective properties (Dragunow & Faull, Trends in Pharmacol. Sci. 7: 194 (1988); Marangos, Medical Hypothesis 32: 45 (1990)). Evidence for AICA riboside-induced enhancement of adenosine levels is both direct i.e. a consequence of measurement of adenosine itself in both animal and cell culture models (Gruber et al, Circulation 80(5): 1400-1410 (1990); Barankiewicz et al, Arch. Biochem. Biophys., 283: 377-385, (1990)) and indirect i.e. implicated by reversal of the anti-ischemic properties of AICA riboside by removal of exogenous adenosine using adenosine deaminase (Young & Mullane, Am. J. Physio., in press (1991)). In hearts subjected to ischemia and reperfusion, cellular damage has been, in part, attributed to plugging of the microvessels by neutrophils. Adenosine has been reported to inhibit neutrophil adhesion to coronary endothelial cells and hence neutrophil accumulation (Cronstein et al., J. Clin. Invest. 78: 760-770 (1986)). Consequently, another feature of the adenosine-mediated protective effects of AICA riboside in the heart can be through prevention of neutrophil-dependent tissue injury in some models of ischemia and reperfusion. This is supported by evidence for decreased accumulation of neutrophils in the ischemic region of the heart by AICA riboside (Gruber et al, Circulation 80: 1400-1410 (1990)).
A recognition of the cardioprotective and neuroprotective properties of adenosine have led to attempts to explore the therapeutic use of exogenously administered adenosine itself. However the short half life of adenosine in blood (<10 secs) necessitates the use of high doses and continuous infusions to maintain levels appropriate for most treatments. Adenosine itself causes hypotension, i.e. reduces blood pressure; it is also a negative chronotropic and dromotropic agent, i.e. reduces heart rate and electrical conduction in the heart, respectively. Adenosine would therefore exert marked systemic hemodynamic effects at concentrations that would be required to elicit cardioprotective or neuroprotective properties. These systemic cardiovascular actions are frequently contraindicated in most clinical conditions where adenosine could be useful. In contrast, as a result of its local effects on adenosine levels, AICA riboside administration does not produce such side-effects, even at doses considerably higher than the expected therapeutic levels (Gruber et al; Circulation 80: 1400-1410, (1990); Young & Mullane, Am. J. Physio., in press, (1991)).
Adenosine receptor agonists have also been studied and effects similar to adenosine have been reported in a number of experimental models. (Daly, J. Med. Chem. 25(3): 197 (1982). Again, because most cell types have adenosine receptors, exogenously administered adenosine agonists exhibit profound actions on a variety of tissues and organs, outside of the target organ, thereby limiting their therapeutic potential.
Other ways of potentially achieving the effect of a high local extracellular level of adenosine have been studied. They include: a) interference with the uptake of adenosine with reagents that specifically block adenosine transport, as described by Paterson et al., in the Annals of the New York Academy of Sciences, Vol. 255, p. 402 (1975); b) prevention of the degradation of adenosine, as described by Carson and Seegmiller in The Journal of Clinical Investigation, Vol. 57, p. 274 (1976); and c) the use of analogs of adenosine constructed to bind to adenosine cell plasma membrane receptors.
There are a repertoire of chemicals that reportedly can inhibit the cellular uptake of adenosine. Some have been reported to do so specifically, and are believed to be essentially competitive inhibitors of adenosine uptake, and others are believed to inhibit nonspecifically. p-nitrobenzylthioinosine appears to be a competitive inhibitor, while dipyridamole and a variety of other chemicals, including colchicine, phenethyalcohol and papaverine appear to inhibit uptake nonspecifically.
U.S. Pat. No. 4,115,641 to Fischer et al. is directed to certain ribofuranosyl derivatives which are said to have cardiac and circulatory-dynamic properties. In particular, Fischer et al. are directed to certain compounds which are said to have intrinsic adenosine-like modes of action as determined by measuring decreased heart rate and blood pressure.
In contrast, AICA riboside and AICA riboside-like compounds lead to enhanced adenosine levels at the specific time and location of a pathological event and thus permit increased adenosine levels to be selectively targeted without the detrimental side effects.
The present invention is directed to AICA riboside analogs which exhibit and, in many cases, improve upon, the positive biological effects of AICA riboside. The novel compounds typically exhibit one or more of the following improvements over AICA riboside 1) functional benefits at lower doses; 2) more potent adenosine regulating actions; 3) increased half-lives or; 4) increased oral bioavailability and/or brain penetration.
Post-surgical complications are a significant source of morbidity and mortality, and healthcare expenditure.
For cardiac surgery, approximately one million patients undergo such every year, and approximately one in six develops a serious major organ complication relating to the heart, brain, kidney, GI tract and lung (Mangano, et al., 1997, J. Intensive Care Med. 12:148-160). Yet despite numerous advances in monitoring and technique, no drug has been shown to reduce or prevent these complications. The preoccupation has been with bleeding, and drugs are now used to prevent such. However, drugs which inhibit bleeding generally cause thrombosis, and therefore may induce ischemia and irreversible organ injury (Cosgrove, et al., 1992, Ann. Thorac. Surg. 54:1031-36).
For noncardiac surgery, approximately 250 million patients undergo such every year, and approximately four percent develop a serious major organ complication relating to the heart (Mangano, et al., 1990, Anesthesiology 2:153-84; Mangano, et al., 1990 NEJM 323:1781-88). Only one drug has been shown to mitigate injury-atenolol (Mangano, et al., 1996, NEJM 335:1713-20). As well, concerns for bleeding predominate, and drugs preventing thrombosis (anti-platelet, anti-clotting) are virtually contraindicated (Eagle, et al., 1999, JACC 34:1262-1347; Pearson, et al, 1994, Circulation 90:3125-33; Baumgartner, et al., 1994, Johns Hopkins Manual of Surgical Care, Mosby Yearbook, St. Louis).
However, for both cardiac and noncardiac surgery, marked excitotoxic and inflammatory responses occur for days after surgery, if not months after surgery (Silicano and Mangano, 1990, Mechanisms and Therapies. In: Estafanous, ed. Opioids in Anesthesia Butterworth Publishers, pp. 164-178). Such markedly exaggerated responses are associated with platelet and clotting factor activation, which may precipitate thrombosis.
Although recognized as a possibility, such agents are relatively—and in some cases (fibrinolytics), absolutely-contra-indicated because of fear of excessive hemorrhage at the surgical site, as well as at other sites (Eagle, et al., 1999, JACC 34:1262-1347; Pearson, et al., 1994, Circulation 90:3125-3133; Baumgartner, et al., 1994, Johns Hopkins Manual of Surgical Care, Mosby Yearbook, St. Louis). Further, some believe—especially after cardiac surgery—that platelet and clotting factor function are depressed after surgery, so that thrombosis is not an issue (Kestin, et al., 1993, Blood 82:107-117; Khuri, et al., 1992, J. Thorac. Cardiovasc. Surg. 104:94-107). Thus, no effort has been made to investigate the use of anti-clotting agents immediately following surgery.
Finally, Applicants have shown that perioperative events manifest over six to eight months or longer (Mangano, et al. 1992, JAMA 268:233-39); thus, continuation of use of such anti-clotting agents throughout the in-hospital, and then post-discharge course, is rational.
Surgery patients—now numbering 40 million per year in the U.S. alone—are aging nearly twice as rapidly as the overall population. (See, Mangano, et al., 1997, J. Intensive Care Med. 12:148-160).
The current standards of care are unsatisfactory to address this critical problem, and novel approaches are desperately needed to prevent post-surgical complications in our aging population.
The electronic monitoring of the fetal heart rate is an important part of the labor and delivery process for women. In some cases, a deceleration in fetal heart rate, including persistent late decelerations with loss of beat-to-beat variability, nonreassuring variable decelerations associated with loss of beat-to-beat variability, prolonged severe bradycardia, sinusoidal pattern, confirmed loss of beat-to-beat variability not associated with fetal quiescence, medications or severe prernaturity, can require emergency intrauterine fetal resuscitation and immediate delivery. (Sweha, et al., 1999. American Family Physician 59(9):2487-2507; Kripke 1999, American Family Physician 59(9):2416). There is a need for methods to prevent or reduce adverse effects from these events for the health of the fetus.